The instant invention relates to a multi-axle vehicle having a front axle and two rear axles, the first rear axle being a drive axle and the second rear axle being a liftable following axle. More particularly, the instant invention relates to a vehicle of this type which is provided with a regulating system for regulating the supply of pressure medium to the brake cylinders associated with the wheels of the vehicle.
A vehicle of the above-mentioned type is known from DE-PS 31 01 731 (U.S. Pat. No. 4,460,220 which is incorporated herein by reference). In this known patent, a pneumatic braking mechanism is disclosed in which the brake cylinders of the following axle are jointly controlled with the brake cylinders of the drive axle. In this vehicle, the first rear axle is a sensing drive axle, i.e., the wheels on this axle are provided with rotational-speed sensors, while the second rear axle is a non-sensing following axle. Therefore, while ABS regulation is in effect, the wheels on the following axle are controlled by the drive (sensed) wheels.
In order to ensure that locking of the wheels on the following axle is prevented when ABS regulation is in effect, the pressure level supplied to the wheels on the following axle is lowered by an intermediary reduction valve. This action causes the wheels on the following axle to be braked with less than full force. The resulting slightly longer braking distance is accepted for the sake of vehicle stability and tire care.
In a commercial vehicle with a liftable following axle, the brake linings on the wheels of the following axle normally wear much more slowly than the linings on the other wheels because the linings on the following axle are not subjected to wear in the lifted state. Such a difference in the extent of wear of the brake linings is not desirable, however, since it is more efficient to replace all brake linings at the same time when the vehicle is being serviced in the workshop.
The instant invention has as its object to ensure approximately even wear of all brake linings in a vehicle with a liftable following axle.